Metallurgical vessel

ABSTRACT

A metallurgical vessel having a tap hole containing a plug comprised of a hardened composition comprising a granular inorganic oxidic material other than glass powder and 1 to 30 weight percent, based on the weight of said material, of glass powder, especially a composition additionally containing a hardenable thermo- or cold-setting phenolic resin, which composition does not disintegrate at high temperatures and retains compressive strength.

This is a division of application Ser. No. 546,832, filed Feb. 3, 1975,now U.S. Pat. No. 4,036,798.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to compositions containing granular inorganicoxidic materials which resist the adverse effects of high temperaturesand which retain at temperatures above 500° C. compressive strength.This invention is particularly directed to compositions containing agranular inorganic oxidic material which at temperatures above 500° C.have increased compressive strength. This invention is also directed tothe use of such compositions as plugs for tapping holes in vesselsemployed for metallurgical refining and in fabricated products,particularly those used in the construction industry, includingpartitions, facings and the like.

2. Discussion of the Prior Art

It is known to prepare moldings and compositions which consist ofoxidic, inorganic additives, such as quartz gravel, quartz flour, orinorganic light substances such as expanded clay, expanded mica,expanded shale and so forth, and of a binder consisting of a thermosetsuch as phenolic resin, epoxy resin, polyester resin and the like, andwhich are used as building materials, in residential construction, forexample. It has also been proposed to use these compositions inconjunction with tar binding agents as ramming compositions or as troughlining compositions and tap hole plugging compositions in metallurgicalinstallations, e.g., for the lining of molds or of troughs.

The thermosetting and/or acid setting compositions that have becomeknown hitherto on the basis of hard, granular, inorganic oxidicsubstances bound by phenolic resins, however, result in hardenedproducts, for residential construction and for hardened linings andseals for metallurgical purposes, for example, which have a number ofimportant disadvantages.

The organic binder in the hardened moldings or linings or seals has theproperty of becoming more or less completely pyrolyzed or coked orconverted to ash under the prolonged direct action of flame or merelyunder the prolonged action of elevated temperatures. Evenflame-resistant organic binding agents have this disadvantage.Accordingly, the fabricated products disintegrate more or less rapidlyunder the action of fire and/or heat, depending on the temperature andduration of such action, because the burning of the synthetic resinbinding agent greatly diminishes or completely destroys their cohesion,i.e., their stability of shape, and their compressive strength.

The term "fabricated products" as used herein is to be understood torefer to construction materials such as partitions, facings and the likein home construction, and linings and seals for metallurgicalinstallations, such as linings for troughs and molds as well as tap holeplugs and the like, in the hardened state.

To improve the stability of shape of hardened construction materialsmade from hard, granular inorganic oxide materials, especially porousones, under the action of fire and/or high temperatures, it haspreviously been proposed to add alkali silicates, silicic acid esters,boric acids and their salts, triphenylborate, or other boron compoundswhich bind themselves to metal oxides under the action of heat and, insome cases, pressure, to mixtures containing phenolic resins, forexample, as binding agents, before they are fabricated and hardened(German "Offenlegungsschrift" No. 1,571,399).

In these known construction materials, especially when porous hardmaterials are used as additives, it is disadvantageous that theircompressive strength decreases under the action of heat and/or fire.

It is indeed possible to improve sound insulating properties byreplacing the porous hard materials with non-porous hard materials asadditives. By such measures the compressive strength of the hardenedconstruction materials is improved. Nevertheless, it has hitherto beenimpossible to achieve the objective of replacing a partition built up byconventional methods of approximately 12.0 centimeter bricks with apartition approximately 3 to 5 cm thick having approximately the sameheat and fire resistance and made of the previously known thermosettingand/or acid-setting compositions containing inorganic oxide additivesand a binding agent of phenolic resin.

When hardenable compositions are used for metallurgical purposes, e.g.,as compositions which can be rammed onto troughs or compositions for thelining of the inner surfaces of ingot molds or for tap hole pluggingcompositions, it is desirable to have sufficiently great stability ofshape combined with compressive strength in the fabricated productsunder the action of heat or flame, as the case may be. The molten metalswith which the compositions or fabricated products come into contact, inthe tapping of a blast furnace for example, are usually at temperaturesgreater than 500° C. up to about 1800° C. The thermal stress is thussubstantially greater than it is in a burning house, for example (in aresidential fire the temperatures are generally reckoned at up to 800°C., though the temperatures locally may be lower, e.g., below 500° C.).

The fabricated products made from the known compositions, however, donot meet these requirements, since their compressive strength and theirstability of shape are insufficient at the high temperatures involved.

The life of protective coatings in troughs or molds, when made from thecompositions heretofore known, is relatively short. In most cases,cracking and spalling or partial decomposition is found after as littleas a single use, so that the linings have to be renewed.

Especially problematical is the use of the previously knownthermosetting compositions of the above-named type as tap hole pluggingcompositions. Tap hole plugging compositions have to meet particularlyhigh requirements in practice. On the one hand, after they have set,they must withstand the high ferrostatic pressures and the relativelyhigh temperatures (usually over 1000° C.) without disintegrating. Theymust shrink as little as possible. On the other hand, the plugs must beremovable at the end of the smelting process. Consequently, they mustnot be excessively resistant to pressure. Thus, they must have maximumstrength in order to withstand the pressures and temperatures prevailingin the metallurgical vessel.

Accordingly, it is an object of the present invention to provide acomposition which can be employed in the construction industry whichdoes not burn or disintegrate or lose its compressive strengthsubstantially upon being subjected to temperatures, say, of 500°-1000°C. It is another object of the invention to provide a hardenablecomposition which can be used in the metallurgical industry as a rammingcomposition for troughs or as a liner for inner surfaces of ingot moldsor as a plug for a tap hole, which composition does not disintegrate orsubstantially lose its compressive strength when subjected totemperatures of 500°-1800° C. It is a particular object of the inventionto provide a hardenable composition whose compressive strength willincrease when it is subjected to temperatures above 500° C.

SUMMARY OF THE INVENTION

These and other objects of the invention are provided by a compositioncomprising a granular inorganic oxidic material other than glass powderand 1 to 30 weight percent, based on the weight of said material, ofglass powder. The composition of the present invention can also containa hardenable thermo- and/or cold-setting composition, particularly ahardenable phenolic resin, especially a hardenable phenolic resin of thenovolak type. In accordance with the invention it has been discoveredthat if inorganic oxidic compositions in granular form are modified bythe inclusion of 1 to 30 weight percent of glass powder, the compositionhas a surprising resistance to the degradative effects of temperaturesabove 500° C. Thus, it has been found that whereas compositionscomprising a major amount of granular inorganic oxidic material and ahardenable resin will disintegrate at temperatures of 500° C., acomposition which additionally contains 1 to 30 weight percent of aglass powder will resist disintegration. Depending on the amount ofglass powder included in the composition, the compressive strength canactually increase at temperatures above 500° C.

There are provided, in accordance with this invention, compositionswhich when hardened form fabricated products of high density andimproved stability of shape and compressive strength, and which alsoduring and after the application of heat and/or pressure have minimumstrengths such as those required in applications in which thecompositions or fabricated products are or may be exposed totemperatures of approximately 500° to 1800° C.

The problems inherent in prior art compositions are solved in accordancewith the present invention by including into the granular inorganicoxide composition 1 to 30 weight percent of a glass powder. It should beunderstood that the term "inorganic oxide material," as used herein,contemplates granular inorganic oxide materials other than the powderedglass additive. Thus, the term specifically contemplates materials suchas quartz sand and the like as more specifically set forth below. Itshould be understood that this invention is also directed to the use ofsuch modified compositions for the production of fabricated products.

Suitable hard, granular inorganic oxide materials are those having ahardness greater than 6, and preferably of 7 to 9 on the Mohs scale ofhardness. Quartz sands of various origins are used preferentially.However, other sands of mineral origin may be used, such as zirconiumsand or sands containing, in addition to SiO₂ and alkali oxides, Al₂ O₃and/or MgO and/or CaO, and other such sands. Synthetic granular hardsubstances can be used, such as fused mullite, fused spinel,electrocorundum and the like. Mixtures of "mineral" sands with synthetichard substances can also be used. "Mineral" in the context of "mineralsands" refers to SiO₂ -containing natural sands being resistant to hightemperatures.

Fundamentally, porous inorganic oxide hard materials can also be used oradded, such as for example expanded clay, expanded mica, expanded shaleand the like, if good thermal insulation is to be achieved, in buildingmaterials for example, such as in the outside walls of a house. Inpartition wall components, however, it is desirable, for better soundinsulation, not to use porous hard materials. In the case ofcompositions which are to be used for metallurgical purposes, it is alsodesirable to avoid the use of porous hard materials, so as to achievethe greatest possible density and thermal stability in the fabricatedproduct.

The grain size of the hard, inorganic oxide substances can vary widelyand is broadly between 0.05 and 2.0 mm. Preferred are grain sizesranging from about 0.5 to 0.1 mm, it being possible to use individualgrain size fractions within this range or mixtures of grain sizefractions.

In some cases, however, more coarsely granular hard materials can beused, e.g., those of grain sizes ranging from 1 to 0.5 mm. For manyapplications a quartz sand of the following grain size distributionproves desirable:

1 to 15 weight percent, especially 8 weight percent = 0.1 to 0.2 mm

40 to 80 weight percent, especially 63 weight percent = 0.2 to 0.315 mm

10 to 50 weight percent, especially 29 weight percent = larger than0.315 mm.

A great variety of pulverized glasses can be used as the powdered glass.For the purpose of the invention, for example, those glasses whichcontain about 12 to 18 weight percent alkali oxides and about 10 to 30weight percent alkaline earth oxides are suitable, the balanceconsisting essentially of SiO₂ and, if desired, subordinate amounts ofother metal oxides.

A preferred embodiment of the invention consists in using those glasspowders which soften at temperatures of approximately 600° to 1000° C.,preferably at about 800° C.

A glass powder having a grain size distribution of >0 to 100 microns isused preferentially. Individual grain size fractions within this rangecan also be used. Fundamentally it is also possible to use coarser glasspowders, such as for example those having a grain size distribution of100 to 200 microns.

DESCRIPTION OF PREFERRED EMBODIMENTS

The composition of the present invention desirably employs a hardenableresin such as a hardenable thermosetting and/or cold-setting resin,particularly a hardenable phenolic resin of the novolak type. Thephenolic resin binding agent which can be used in accordance with theinvention can be any phenolic resin of the resol type in solid, powder,liquid or dissolved form, or also novolak-hexamethylenetetraminemixtures in the dissolved or powdered state.

Suitable phenolic resins of the resol type are obtained, for example, bythe condensation of one mole of a phenol with one to three moles ofaldehydes in an alkaline medium, followed by vacuum distillation of thewater and, in some cases, adjustment of the pH value to a value greaterthan 4. The phenols may be not only phenols but also their homologs suchas the cresols and resorcinols, and xylenols, or mixtures of thesecompounds. The aldehydes which react with the phenols include, amongothers, formaldehyde, compounds which break down to formaldehyde such asparaformaldehyde or trioxane, acetaldehyde, furfurol andhexamethylenetetramine, etc., and mixtures of these compounds. Thecondensation is performed in an aqueous, alkaline medium. The resols canbe used in solid form, in aqueous liquid form, or in alcoholic solution.

Phenolic resins of the novolak type are obtained, for example, bycondensing a phenol with an aldehyde in a molar ratio of 1:0.75 to 1, inthe presence of acids such as sulphuric acid, oxalic acid, hydrochloricacid, dilute hydrochloric acid or acid salts. The water that is splitoff is removed by distillation in vacuo.

The setting of the novolaks is best performed by the addition ofhexamethylenetetramine or other formaldehyde yielding substances attemperatures above 100° C. The setting of the phenolic resins of theresol type can be performed by the action of heat, the temperaturesgenerally ranging from 100° to 180° C. They may also be set, however, byacids alone or with the simultaneous input of heat at temperatures lowerthan 25° C. In general, acids are used, such as for example mineralacids, formic acid, acetic acid, oxalic acid, water-soluble sulfonicacids in which the sulfonic acid group is attached directly to anaromatic ring, which can be substituted if desired. Examples are:benzenesulfonic acid, p-toluenesulfonic acid,chlorobenzene-3,5-disulfonic acid, bromobenzene-4-sulfonic acid, ortho-,meta and para-cresolsulfonic acids or aniline-2,5-disulfonic acid. Thesulfonic acid group can also be linked to a polynuclear aromaticradical, as in the case, for example, of the naphthenesulfonic acids orthe naphthylaminesulfonic acids.

The aqueous solutions of these acids are used mainly as 20 to 70 weightpercent solutions. A number of acids, such as p-toluenesulfonic acid forexample, can also be used in pulverized form as a hardener. The amountof hardener used generally ranges between 1.0 and 15.0 weight percent,preferably 1 to 5 weight percent, reckoned as 100% acid, with respect tothe solid content of the phenolic resin.

The hardening can be performed during or after the shaping operation,either at elevated pressure or at normal pressure.

For the preparation of the compositions of the invention, the additivesthat are to be used (granular, inorganic oxide hard materials pluspowdered glass) and other additives if desired, such as, for example,hardeners, fluxes and the like, are intimately mixed with the resols ornovolaks in suitable mixing means, such as kneaders or roller mixers orconcrete mixers. The proportion of the phenolic resin to be put in isbest selected such that the ratio of phenolic resin (determined as solidresin) to inorganic oxide materials amounts to from 1 to 20:99 to 80percent by weight, preferably from 3 to 8:97 to 92 percent by weight. Ifdesired, the mixing units can be heated.

The composition can then be compressed in molds, preferably steel molds,and hardened at about 80° to 250° C., preferably 150° to 170° C., eitherat elevated pressure, e.g., more than 150 kp/cm², or at normal pressure,to form the fabricated products such as structural components for wallelements or facings in residential construction. The hardening time willdepend on the reactivity of the binding agent, on the settingtemperature, in some cases on the concentration of the hardener and onthe wall thickness of the fabricated product. Roughly speaking, thehardening time will generally amount to about one minute per millimeterof wall thickness.

In the lining of a trough in metallurgical furnaces or in the lining ofcasting molds made, for example, of chamotte, a slightly moist tofree-flowing mixture of the resols or novolaks is tamped with tar pitchbinding agents, the additives used in accordance with the invention, anda hardener if necessary, onto the surface to be protected, in thedesired thickness. The hardening can take place then and there beforethe lining is put in operation, e.g., when phenol resins of the resoltype are used, by heating the coating to the setting temperature, e.g.,130° to 170° C. at normal pressure. In many cases it is not essential toperform the complete hardening before the lining is put in operation, ifthe hardening takes place with an input of heat. The hot materialflowing through the trough or into the mold will within a short timeharden the coating during operation. This procedure can be appliedaccordingly also to the sealing of a tap hole of metallurgical furnaces,and to tamping or ramming compositions for metallurgical purposes ingeneral, wherever the compositions are subjected to the action of heatduring use.

Surprisingly, the addition of 1 to 30 weight percent of powdered glassin accordance with the invention permits the production of fabricatedproducts capable of withstanding the action of heat and having a highdensity, high stability of shape and great compressive strength. As itwill be shown by the examples, the compressive strengths are still veryhigh even after 3 hours of heating at 1000° C., while fabricatedproducts which do not contain this additive and which are heated underthe same conditions disintegrate.

Especially surprising is the effect of the addition of 10 parts glasspowder by weight. A compressive test specimen on the basis of 100 partsquartz sand, 10 parts glass powder by weight and 2.5 weight parts of aphenol formaldehyde resin (approximately 72% solid resin content,viscosity about 800 cP) has a compressive strength of 35 kp/cm² after 45minutes of exposure to a heat of 160° C. After 3 hours of heating at1000° C., the compressive strength, however, rises to 111 kp/cm². Animprovement of the compressive strength of fabricated products afterexposure to heat has been impossible to achieve with the compositionsknown hitherto.

The compositions of the invention are especially capable of good use, onaccount of the high resistance to heat of fabricated products madetherefrom, in those applications in which minimum compressive strengthsduring or after the action of high temperatures -- temperatures of about800° C. to 1800° C. -- are required of such fabricated products. Theycan therefore be used as ramming compositions, for example, forbackfilling metallurgical furnaces or for the lining of troughs or ingotmolds, or for tap hole plugging compositions and the like. If desired, aportion of the phenolic resin binding agent can be replaced by anotherorganic binding agent such as tar pitch, in these applications.

An additional advantage of the compositions of the invention consists inthe fact that, by varying the quantity ratios of the essentialcomponents of the mixture, i.e., the glass powder, the granularinorganic oxide materials and the phenolic resin, the products madetherefrom can be adapted to quite specific minimum strengths or also toquite specific maximum strengths. Such adaptation of the compositions tothe requirements which they have to meet in use is especially importantin the case of tap hole plugging compositions. For example, compoundscomposed of 5 weight percent glass powder, 90 weight percent quartz sandand 5 weight percent phenolic resin have proven valuable in practice,the phenolic resin being able to be replaced with a mixture of phenolicresin and tar pitch if desired, depending on the application. However,compositions which contain at least 10% by weight of glass powder arecharacterized by having increased compressive strength after beingsubjected to temperatures of 1000° C., e.g., after being subjected totemperatures of 1000° C. for 3 hours.

For many applications it is desirable to add to the compositions, inaddition to the granular inorganic oxide materials and the glass powder,fluxes such as powdered boron compounds, such as for example boricacids, boron trioxide, alkali or alkaline earth borates, or mixtures ofsame.

The preferred boron compound is sodium tetraborate. Surprisingly, when0.1 weight part of sodium tetraborate is added to a mixture of 100weight parts of quartz sand, 2.5 weight parts phenolic resin (solidresin content 72 weight percent) and 1 part by weight of glass powder,the compressive strength of a test specimen heated for 3 hours at 1000°C. is five to eight times higher than the compressive strength of a testspecimen which does not contain this addition of sodium tetraborate.

As an advantageous embodiment of the invention, therefore, compositionsare proposed which additionally contain 0.1 to 3.5 weight percent ofinorganic boron compounds, preferably sodium tetraborate, with respectto the hard, granular inorganic oxide substances.

If desired, instead of the boron compounds or in addition thereto thecompositions of the invention can contain alkali carbonates, preferablysodium carbonate, in amounts of 0.1 to 5% of the weight of the hardgranular inorganic oxide substances. For example, the compressivestrength of a test specimen based on a mixture of 100 weight parts ofquartz sand, 2.5 weight parts of phenolic resin (solid resin contentabout 72 weight percent), 5 weight parts of powdered glass and 3.5weight parts of sodium carbonate is 13 kp/cm² higher after 3 hours ofheating at 1000° C. than the compressive strength of a test specimen ofthe same mixture components without the addition of the sodiumcarbonate. The addition of the alkali carbonates brings with it theadvantage that they diminish the melt viscosities of the compositions ofthe invention, if desired. In the case of the thermosetting compositions(without the addition of acid) the use of alkali carbonates ispreferred.

The compositions containing boron and/or alkali carbonates arepreferentially used for the manufacture of those fabricated products inwhich temperatures of less than about 800° C. might be produced by theaction of flames and/or heat. Temperatures of less than about 800° C.can be observed, at least locally, in the burning of a house. Forreasons of safety, it is therefore desirable to use, especially forinternal partition walls in residential construction, those compositionswhich soften below the softening ranges of the glass powders used. Thelowering of the softening range or of the melt viscosity, as the casemay be, can be achieved by the addition of the inorganic boron compoundsand/or alkali carbonates. In this manner it is possible to prevent wallelements from collapsing prematurely due to the fact that the organicbinding agent, namely the phenolic resin, is partially or completelyburned up before its binding function can be taken over by the inorganiccomponents, for it is theorized that the glass powder, plus the boroncompounds and/or the alkali carbonates, if used, combines withcomponents of the hard granular inorganic oxide substances to formflame-resistant and heat-resistant, enamel-like substances which largelytake over the binding function of the hardened organic binding agentduring or after the destruction of the latter by combustion.

Therefore, for the production of building materials, especially ofinternal partition walls, face paneling and the like, thosethermosetting and/or acid-setting compositions on the basis of hardgranular inorganic oxide substances bound by phenolic resins inaccordance with the invention are preferred which contain inorganicboron compounds and/or alkali carbonates in the stated amount inaddition to the glass powder.

As hard granular inorganic oxide substances for internal partitionwalls, non-porous hard substances are preferred, especially quartz sand.

The wall components prepared from such compositions are verycompression-resistant after they have set, and they have a high density.In their compressive strength and in their density, both after andduring the action of flames or heat, they are superior to the previouslyknown wall components prepared in a similar manner. Their soundinsulating qualities are good. On account of their high compressivestrength and sound stopping qualities, they are able with a thickness of4 cm, for example, to replace a conventional masonry brick wall of athickness of about 12.0 cm.

If, for example, construction materials of higher thermal insulation arerequired, it is basically possible to use porous granular inorganicoxide substances such as expanded clay, expanded shale, expanded micaand the like instead of or together with the non-porous granularinorganic oxide substances, preferably quartz sand.

In order to more fully illustrate the nature of the invention and themanner of practicing the same, the following examples are presented.

EXAMPLES

The following raw materials were used:

1. Quartz sand (source: Haltern; type H 32)

Grain size distribution:

8 wt.-% 0.1 to 0.2 mm

63 wt.-% 0.2 to 0.315 mm

29 wt.-% larger than 0.315 mm

2. A liquid phenol-formaldehyde resin (phenol-resol resin) obtainablecommercially under the name "Phenolharz T 77" and having a solid resincontent of about 72 wt.-% and a viscosity of approximately 800 cP.

3. A powdered glass of a fineness of 0 to 100 microns.

4. Finely powdered sodium tetraborate.

5. Anhydrous, pulverized sodium carbonate.

EXAMPLES 1-5

The experimental data and findings listed in Table 1 clearly show theeffect achieved by the invention.

The experiments were performed as described herewith: H 32 quartz sand,phenolic resin binding agent and the additives of the invention in theform of powdered glass, plus boron compounds and alkali compounds insome cases, were mixed intimately together in a suitable mixer, such asa concrete mixer, for 10 minutes, and 6 compressive testing specimens 50mm in diameter and 65 mm long with a density of approximately 1.50g/cm³, were prepared from each of the mixtures using a GF ramming andmolding apparatus. The specimens were hardened in a circulating air ovenat atmospheric pressure with heat alone at 150°-170° C.

After cooling, the compressive strength of three specimens was tested bymeans of a GF compressive testing apparatus. The other three testspecimens of the same raw material mixture were placed in a mufflefurnace for 3 hours at about 1000° C. and after cooling they were testedfor residual compressive strength and dimensions (stability of shape).

                                      TABLE 1                                     __________________________________________________________________________    Experimental Example No.                                                                           1      2   3   4   5   6                                 __________________________________________________________________________    Composition of Test                                                           Specimens                                                                     Sand H 32       (kg) 100    100 100 100 100 100                               Phenolic resin T 77                                                                           (kg) 2.5    2.5  2.5                                                                              2.5 2.5 2.5                               Glass powder    (kg) --     5.0 10.1                                                                              1   1   5.0                               Sodium tetraborate                                                                            (kg) --     --  --  --  0.1 --                                Sodium carbonate                                                                              (kg) --     --  --  --  --  3.5                               Characteristics of                                                            the Test Specimens                                                            Compressive strength                                                          (after 45 minutes                                                                             (kp/cm.sup.2)                                                                      140    140  35 140 140 140                               at 160° C)                                                             Compressive strength                                                          (after 3 hours at                                                                             (kp/cm.sup.2)                                                                      disintegrated                                                                         67 111  3   20 80                                Density direct/             1.56                                                                              1.56                                                                              1.56                                                                              1.56                                                                              1.56                              density after 3 (g/cm.sup.3)                                                                       disintegrated                                            hours at 1000° C     1.51                                                                              1.51                                                                              1.51                                                                              1.51                                                                              1.51                              Dimensions: height(mm) direct                                                                             65 mm                                                                             65 mm                                                                             65 mm                                                                             65 mm                                                                             65 mm                             (after 3 hours at    disintegrated                                            1000° C)             65 mm                                                                             65 mm                                                                             65 mm                                                                             65 mm                                                                             65 mm                             __________________________________________________________________________

What is claimed is:
 1. A metallurgical vessel for carrying out ametallurgical refining process, said vessel having a tap holeaccommodated by a plug, said plug comprising a hardened compositionconsisting essentially of an inorganic oxidic material other than glasspowder and 5 to 30 weight percent of glass powder having a particle sizeof >0 to 100 microns and 1 to 20 weight percent of a hardenable thermo-or cold-setting phenolic resin, the weights being on the basis of theweight of the inorganic oxidic material.
 2. A metallurgical vesselaccording to claim 1 wherein said inorganic oxidic material is sand. 3.A metallurgical vessel according to claim 2 wherein said sand is quartzsand.